Google is preparing the different UIs in order to take advantage of every possible screen size that could be featured on a tablet or smartphone.

Applications will normally scale automatically to any sized screen, but sometimes will much better on larger ones if the developer creating them has used Android SDK tools properly.

Interaction metaphors used on phones or on 10-inch tablets may not be best for a 7-inch tablet, according to Google, who has added in an extra UI for that-sized device.

The Nexus 7's JellyBean layout uses the pull-down notification shade that is featured on other Android phones, but also has the paneled app layouts that normally come on an Android tablet. The device was originally expected to use the UI created for smartphones, but actually features its own custom version of the operating system.

Smartphones, 7-inch, and 10-inch tablets will all have their own unique layout of the operating system.

The first smartphone to begin receiving the Android 4.1, JellyBean update was the Samsung Galaxy Nexus.

The upgrade began rolling out earlier this week and is available over-the-air for HSPA+ Galaxy Nexus models. Owners of the handset should have been prompted to perform the update sometime in the past few days.

JellyBean was introduced at Google I/O at the end of last month. The software has many new features including a revamped notifications system, and a Siri competitor known as Google Now.

It also has a redesigned search experience with a new user interface and an improved Voice Search.

Google Now works as an artificial assistant that can answer commonly asked questions such as what the weather will be, how much traffic to expect, or the score of a sports game.

The next devices scheduled to receive Jellybean includes the Nexus S, and Motorola XOOM tablet.